Moldmaking HELP! Need tips for plaster molds

Making A Plaster Mold Using A Hard Boiled Egg

The best way to quickly get up to speed making multiple-piece plaster molds, is to make some plaster molds.
I recommend Making A Plaster Mold Using A Hard Boiled Egg to learn how to make a two-piece plaster mold.
A hard-boiled egg is small, and inexpensive. Also, it is unforgiving.
If you don't get the parting line just right, it is locked in one half of the mold.
Still, it is much better to practice learning how to make plaster slip casting molds, by actually making molds.
An egg is small, and relatively inexpensive, so the plaster molds can also be small.
You won't worry about using a lot of plaster, or messing up doll parts.
Plan on making some mistakes. Learn is spelled F-A-I-L.
Plan on making several molds in order to learn. Give yourself enough time to do it.
So buy some No.1 Pottery Plaster, get some clay for making the build-ups, and make some coddles.
You'll also need some clamps to hold the coddles together, and some rubber bands to band the molds for pouring.
Mix some water and liquid soap together to make some parting agent.
You'll need a soft brush or elephant ear sponge to apply the parting agent to the plaster.
Get all your tools and materials together ahead of time.
Being prepared is the best way to keep the stress level to a minimum.
Spread out some old newspapers to catch the mess.
Have a trash can, lined with old newspapers, ready to dump excess mixed plaster into.
Get a 5-gallon bucket, half-filled with water to rinse your hands and tools and mixing bowls.
NEVER put plaster (dry, wet, or set) into the drain pipes !!!
You'll also need some good scales for weighing plaster and water.
When I was learning how to make plaster molds, I always found it helpful to make a step-by-step checklist.
Remember, plaster mold making is a Craft Skill, so expect a learning curve, okay?
Try to have fun, because you learn more that way.

Here are some more helpful links:
plaster-mold-refresher.html
plaster-mold-making.html
Martha Armstrong-Hand's Method @ WES

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I'm guessing the parting lines are a big concern to you-- this tutorial helped me a lot with that (to a point. The pencil-around-the-object method works well with two-part molds, anything more than that and it gets complicated.) Good luck! Let us know how it goes.

 

Check and see if your (college or public) library has a copy of Plaster Mold and Model Making by Charles Chaney and Stanley Skee (ISBN: 0442215118). That book is MY Plaster Mold Making Bible.

One last thought: Give yourself enough time for the slip casting molds to dry thoroughly. Plaster slip casting molds work by sucking moisture from the slip, causing the slip to thicken around the walls of the mold. The excess slip is poured back into the slip jug when the thickness of the casting is what you want, leaving a hollow casting. The molds should be banded together during this drying process, because plaster molds can warp during drying. It is a good idea to prop the molds up on blocks or something similar to allow air to circulate all around the molds during drying. Turning the molds frequently, also helps drying. A small electric heater with a fan can also help when drying the molds. Make sure the heater is not too close to the drying molds, so they do not get too hot.

On page 48 of Learning To Be A Doll Artist, Martha Armstrong-Hand writes:

I dry my molds near a gas heater, propped up so air can get at all sides, and I turn them every few hours. When the weather allows it, I also set them outside on a bench in the sun, turning them often.

A mold should be completely dry before porcelain slip casting takes place. However, molds must never be dried forcefully with too much heat as in a home oven, and air should get to them so they dry evenly from all sides.

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Yeah, okay, so eggs are ubiquitous, and are relatively inexpensive, small, and so forth, but are they useful for doll-making?
This is a series of posts about making a plaster mold for casting carving wax balls (spheres), using a 40mm ping-pong ball as a pattern:
31
32
33
34
35
and here is a post about making spares:
spares

Yeah, so plaster mold making IS a Craft Skill... there are SO many details.
Every mold you make is different, in some way or another.
Making sculpture is all about Problem Solving.
Right?

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I love the Making a Mold with a Hard Boiled Egg as well. You can also check this out...

Making Molds for Porcelain Slip Casting